1. Field of the Invention
The present invention relates to a thin film magnetic head comprising two coil layers formed between core layers, and particularly to a thin film magnetic head capable of improving stability of a DC resistance value between the two coil layers and maintaining good conductivity between the two coil layers, and a method of manufacturing the magnetic head.
2. Description of the Related Art
A magnetic head device mounted on a hard disk device or the like comprises a thin film magnetic head formed on the trailing-side end surface of a slider and comprising, for example, a reproducing MR head and a recording inductive head.
The inductive head comprises lower and upper core layers each made of a magnetic material, and a coil layer for inducting each of the core layers so that a magnetic signal is recorded on a recording medium such as a hard disk or the like by a leakage magnetic field from a gap layer between both core layers.
The structure of the thin film magnetic head is improved many times for complying with a narrower track with increases in the recording density in future. FIG. 24 is a longitudinal sectional view showing an example of the thin film magnetic element.
In FIG. 24, reference numeral 1 denotes a lower core layer made of a magnetic material such as permalloy or the like. In the surface facing a recording medium, a pole portion 6 comprising a lower pole layer 2, a gap layer 4 and an upper pole layer 5 is formed. As shown in FIG. 24, a Gd-determining insulating layer 10 is formed between the lower core layer 1 and the pole portion 6 so as to be located behind the surface facing the recording medium in the height direction.
As shown in FIG. 24, a coil insulating under layer 11 is formed on the lower core layer 1, and a first coil layer 12 is formed on the coil insulating underlying layer 11. Assuming that the upper surface of the upper pole layer 5 is a reference plane A, the upper surface of the first coil layer 12 is lower than the reference plane A. Furthermore, a coil insulating layer 15 is formed on the first coil layer 12 so that the upper surface of the coil insulating layer 15 and the reference plane A lie in the same plane.
As shown in FIG. 24, the coil center 12a of the first coil layer 12 is behind, in the height direction (the Y direction shown in the drawing), a back gap layer 13 made of a magnetic material and formed on the lower core layer 1.
Also, a raised layer 14 is formed below the coil center 12a with the coil insulating underlying layer 11 provided therebetween. The upper surface of the coil center 12a is formed at a position higher than the upper surface of the conductor of the first coil layer 12 due to the presence of the raised layer 14. Referring to FIG. 24, the upper surface 12b of the coil center 12a and the reference plane A lie in the same plane so that the upper surface 12b is exposed from the upper surface of the coil insulation layer 15.
In this thin film magnetic head, a second coil layer 16 is spirally formed on the coil insulating layer 15. As shown in FIG. 24, the coil center 16a of the second coil layer 16 is conductively connected directly to the coil center 12a of the first coil layer 12 which is exposed from the upper surface of the coil insulating layer 15.
Also, as shown in FIG. 24, the second coil layer 16 is covered with an insulating layer 17 made of an organic insulating material. Furthermore, the upper pole layer 5, the insulating layer 17 and the back gap layer 13 are coated with an upper core layer 18 formed by, for example, a frame plating method.
As described above, the thin film magnetic head shown in FIG. 24 has a structure adaptable to a narrower track, but a coil layer having a two-layer structure enables a decrease in the width dimension of the first coil layer 12 formed between the pole portion 6 and the back gap layer 13, as compared with a coil layer having a single-layer structure. Therefore, the length from the tip 18a of the upper core layer 18 to the base end 18b can be shortened to shorten the magnetic path from the upper core layer 18 to the lower core layer 1, thereby decreasing the inductance of the inductive head.
FIGS. 25 to 27 are drawings showing the steps of a method of forming the raised layer 14 on the lower core layer 1 and forming the coil center 12a of the first coil layer 12 on the raised layer 14.
In FIG. 25, a resist material is coated on the lower core layer 1, and then cured by heat treatment to form the raised layer 14. Also, the coil insulating under layer 11 is formed on the lower core layer 1 and the raised layer 14. Furthermore, a plating under layer 21 is formed on the coil insulating under layer 11.
Next, in FIG. 26, a resist layer 19 is formed on the coil insulating under layer 11, and an aperture pattern 20 is formed in the resist layer 19 above the raised layer 14 by exposure and development, for forming the coil center 12a of the first coil layer 12.
Then, the coil center 12a of the coil layer 12 is formed in the aperture pattern 20 by plating.
In FIG. 27, after the resist layer 19 is removed, the plating under layer 21 is removed except the portion of the plating under layer 21 formed below the coil center 12a. Then, the coil insulating layer 15 made of alumina or the like is formed on the coil insulating under layer 11 and the coil center 12a, and the upper surface of the coil insulating layer 15 is polished by a CMP technique. In this step, the coil insulating layer 15 is polished up to, for example, B—B line coplanar with the reference plane A shown in FIG. 24 to expose the upper surface of the coil center 12a of the first coil layer 12 from the upper surface of the coil insulating layer 15.
However, the structure for conductively connecting the coil center 12a of the first coil layer 12 formed on the raised layer 14 to the coil center 16a of the second coil layer 16 has the following problems.
The polishing step shown in FIG. 27 causes a difficulty in forming the upper surface 12b of the coil center 12a of the first coil layer 12 with a constant exposed area.
In the step shown in FIG. 26, the upper surface 14a of the raised layer 14 is sagged and rounded by the influence of heat treatment for curing. Therefore, the upper surface 12b of the coil center 12a of the first coil layer 12 formed on the raised layer 14 is also rounded following the shape of the upper surface 14a of the raised layer 14.
When the upper surface 12b of the coil center 12a is formed in a curved surface, not a flat surface, as described above, the exposed area of the upper surface 12b of the coil center 12a, which is exposed from the upper surface of the coil insulating layer 15, varies according to the amount of polishing of the upper surface 12b of the coil center 12a during the step shown in FIG. 27. The amount of polishing is determined by the position where the reference plane A shown in FIG. 24 and the upper surface of the coil insulating layer 15 lie in the same plane.
Therefore, in the step shown in FIG. 27, polishing of the coil insulating layer 15, for example, up to B—B line so that the upper surface 12b and the reference plane A lie in the same plane, and polishing of the coil insulating layer 15, for example, up to C—C line so that the upper surface 12b and the reference plane A lie in the same plane are different in the exposed area of the upper surface 12b of the coil center 12a which is exposed from the upper surface of the coil insulating layer 15. Therefore, in the structure in which the coil center 12a of the first coil layer 12 is formed on the raised layer 14, the area of contact between the coil centers 12a and 16a of the first and second coil layers 12 and 16 readily varies with the product, and thus the DC resistance value varies to fail to keep quality constant.
Furthermore, when the coil insulating layer 15 is polished to the C—C line shown in FIG. 27 to significantly decrease the contact area between the coil centers 12a and 16a of the first and second coil layers 12 and 16, conductivity between the coil centers deteriorates.
Also, in the step of the above-described production method shown in FIG. 27, the height of the coil center 12a varies according to the amount of polishing, and the DC resistance value accordingly varies. Therefore, the thickness of the raised layer 14 must be set to a constant value so that the heights of the coil centers 12a of all products are constant after polishing. However, the thickness of the raised layer 14 readily varies according to the heat treatment conditions for curing to cause a difficulty in setting the thickness of the raised layer 14 to a constant value. Therefore, the height dimension of the coil center 12a formed on the raised layer 14 also varies with change in the thickness of the raised layer 14, and thus the height dimension of the coil center 12a readily varies to cause a difficulty in producing products having a constant DC resistance value.
Furthermore, as shown in FIG. 28, when the aperture pattern 20 is formed at a position deviating from the position directly above the raised layer 14 during exposure and development of the resist layer 19, the shape of the coil center 12a of the first coil layer 12 formed in the aperture pattern 20 varies according to the position where the aperture pattern 20 is formed. Therefore, the exposed area of the upper surface 12b and the height dimension of the coil center 12a of the first coil layer 12 vary with the product, thereby failing to stabilize the DC resistance value.
As described above, the structure for conductively connecting the coil center 16a of the second coil layer 16 to the coil center 12a of the first coil layer 12 formed on the raised layer 14 has the problems of failing to obtain a stable DC resistance value and causing a difficulty in achieving good conductivity.
The above-described problems of variation in the DC resistance value and poor conductivity also readily occur between a bump and a lead layer formed below an external connecting terminal.